The present invention relates to a recording substrate having a void structure and production technique of the same. More specifically it relates to a recording medium advantageously effective to form a high quality image employing an ink jet recording system, and a production technique of the same. In more detail, the present invention relates to a technique to enhance ink image receptivity of substrate having support such as paper, plastic film, and the like by applying a discharge plasma treatment under atmospheric pressure or near atmospheric pressure to said supports.
Ink jet systems, in a broad sense, include, for example, a bubble jet method, a piezo electrode method, and the like. Printers utilizing such systems are low in cost as well as resulting in less operating cost, compared to laser printers utilizing an electrostatic recording system. Thus, a number of ink jet printers for consumer use are being marketed and development for such printers is increasingly progressing.
As is commonly known, an ink jet system utilizes a technique in which ink is ejected from a fine opening followed by allowing the resulting ink droplets to contact a recording medium to form an image. Further, in the present invention, in describing the behavior of ink droplets which reach an image receiving surface of a recording medium and form an image, xe2x80x9ccollisionxe2x80x9d, xe2x80x9carrivalxe2x80x9d, and xe2x80x9cshotxe2x80x9d are employed to describe the same behavior. Furthermore, during ink jet printing, when image data, other than character data, are specifically printed, a recording medium is required to quickly and efficiently absorb ink droplets so that ink droplets ejected from an ink droplet ejecting unit (occasionally referred to as a printer head) are shot on the right spots and results in no blotting in the surface direction on the image receiving surface.
As recording media for such an ink jet system, plain paper is generally employed. However, with the development of better ink, ink jet printing has been applied to printing of cloth and the like. Further, along with the achievement of high quality due to finer ink droplets, multicolor, and higher quality obtained by more precise position control of the printing head, ink jet systems have recently, been applied to small volume printing with many types, small volume document printing and the like.
Currently, ink jet printers on the market are available which are capable of carrying out high resolution printing such as at least 1,200 dpi, and such type of printers not only carry out detailed printing but also can be provided with a high speed printing function.
Namely, enhancement of image quality as well as an increase in printing speed has been demanded for ink jet printers. Accordingly, research and development have been carried out not only for printers but also for the software to drive said printers, the ink, and the recording media. For example, now, in January 1999, there is a printer for consumer use, which utilizes a minimum droplet having a volume of only 6 pico liters (six trillionth liter).
At the same time, in order to allow the recording medium itself to contribute to improved image quality, exclusive printing paper has been proposed and demand for it has increased.
As described above, in the ink jet system, a method is utilized in which ink is ejected and onto a recording medium. As a result, when the recording medium is readily blotted with ink, image sharpness is degraded. On the contrary, when the recording medium exhibits low affinity with ink or repels ink, it is impossible to form images.
Special recording media which have been proposed or marketed are those in which the ink image receptivity is improved by forming a functional layer comprised of organic materials such as gelatin, PVA, and the like, or inorganic materials (silica, and the like) as the main component which is applied onto the surface of a substrate such as paper, plastic film (PET, PE, PP, PEN, and the like).
However, it is very difficult to control the physical surface properties such as xe2x80x9cwettabilityxe2x80x9d of the interior of voids only by coating methods. Further, quality and performance of inks are different depending on manufacturers, their products and the types of the ink itself. As a result, when compatibility is taken into account, it is difficult to determine a formula of a coating layer which works well with all types of inks. Further, it is not easy to vary the formula to suitably control the ink image receptivity.
Further, there are problems with adhesion and transfer after printing. These are due to the phenomena in which printing ink works just like an adhesive. Specifically, when printed sheets are piled up in close contact, the image receiving surface adheres with another surface. When these are forcibly peeled apart, the printed image is transferred or at the extreme case, the sheet is torn.
Further, due to the increase in printing speed, the ink ejection pitch (the time interval) has become shorter and problems with the generation of xe2x80x9cdisplacementxe2x80x9d have occurred. When an ink droplet is shot onto an image receiving layer and its soaking rate from the surface to the interior is small, as illustrated in FIGS. 13(a), 13(b) and 13(c) an ink droplet 102 is attracted to the previously shot ink droplet 101 which has not yet soaked into the paper surface 201, and the position of the subsequently ejected ink droplet is displaced from the intended position 104. As a result, in the position at which an ink droplet should be present, no ink droplet is placed (no ink droplet is ejected onto the target position), and thus the color reproduction is markedly deteriorated.
Further, enhancement in the image receptivity has resulted in adverse effects. The first adverse effect is a problem with xe2x80x9cstainingxe2x80x9d. For example, when an image receiving layer is touched with fingers, dirt as well as finger prints is attached, or the image receiving layer is subjected to swelling due to moisture absorption and the resulting image is deformed, and the like. The second adverse effect is an increase in xe2x80x9clongitudinal blottingxe2x80x9d. This problem occurs in such a manner that an ink droplet ejected onto the image receiving surface spreads along the surface direction and is mixed with ink droplets ejected onto adjacent positions to cause undesired color mixture.
As described above, the improvement in image receptivity is accompanied with actual problems. At present, however, effective means to solve such problems have not yet been discovered, and all firms are developing recording media employing a trial and error method. For example, in the case of a technique described in Japanese Patent Publication Open to Public Inspection No. 10-193783, a receiving layer with a compact structure is formed and a technique to allow the resulting surface to be hydrophilic is proposed. However, when only the surface is allowed to be hydrophilic, ink droplets are increasingly spread along the surface direction to degrade the quality, contrary to expectations.
Accordingly, the inventors of the present invention have investigated the problem and have revealed that an important factor is that as an ink droplet is ejected onto an image receiving surface, it is readily soaked in, in other words, the important factor is water absorbing capability (in both aspects of volume and rate) in depth of the recording medium. Specifically, it has been found that interference between ink droplets (occasionally referred to as dots) which are ejected to adjacent positions is minimized by increasing the water absorbing efficiency as well as the water absorbing rate through allowing the interior of the void structure to be hydrophilic and thus the recording function of the ink jet method can be enhanced.
Further, it has been found that contrary to making a surface hydrophilic, allowing the uppermost surface to be water-repellent is an effective measure to minimize staining on the paper surface and the like.
Further, it has been found that an ink jet recording medium, in which the surface layer is to be hydrophilic and only its surface is to be water-repellent, exhibits high image receptive capability.
However, regarding the method to enhance the image receptive performance by varying the physical properties of a coating layer, as described above, no means has been found which is capable of readily varying types in response to characteristics of ink economically and effectively. Further, regarding the appearance of xe2x80x9cstainingxe2x80x9d as well as the increase in xe2x80x9clongitudinal blottingxe2x80x9d accompanied with the enhancement in image receptive performance, no solution has been proposed which allows for both to coexist, because the problems are counter to the improvement in the image receptive performance.
Regarding the surface modification of a support, various techniques have been proposed. For example, regarding coating, various techniques have been proposed for improvement in adhesion (film adhesion). Such techniques include a corona discharge treatment, a vacuum glow discharge treatment, a flame treatment, and in addition, an atmospheric pressure plasma surface treatment recently proposed, and the like. In particular, the details of the atmospheric pressure plasma treatment are described in Japanese Patent Publication Open to Public Inspection Nos. 3-143930 and 4-74525, and Japanese Patent Publication Nos. 2-48626, 6-72308, and 7-48480, and the like. The feature is that under atmospheric pressure or pressure near it, plasma is generated by discharging into an atmosphere composed of argon gas or helium gas as the main component, and a support is subjected to surface treatment employing the resulting plasma.
The inventors of the present patent application have confirmed that such surface modifying techniques markedly improve the image receptive performance of the ink image receptive layer, and further solve problems with xe2x80x9cstainingxe2x80x9d as well as the generation of xe2x80x9cdisplacementxe2x80x9d, and thus the present invention has been achieved.
However, the plasma treatment has problems in which plasma generating conditions are difficult and control of the process is difficult.
Further, during the plasma treatment, the moisture in the reaction gas contributes to the substitution of a functional group. When the moisture content is increased to enhance the substitution efficiency, problems have occurred in which the output of the power source decreases and discharge is not stable.
Means to solve these problems have been investigated. As a result, highly effective conditions for the improvement of an ink receptive layer regarding the control of plasma were discovered.
Namely, a first object of the present invention is to enhance the image receptive performance of a recording media for the ink jet method, employing a surface modifying method.
A second object of the present invention is to minimize or solve problems with xe2x80x9cstainingxe2x80x9d of a recording medium for the ink jet method, employing a surface modifying method.
A third object of the present invention is to minimize or eliminate the generation of xe2x80x9clongitudinal blottingxe2x80x9d of a recoding medium for an ink jet method, employing a surface modifying method.
A fourth object of the present invention is to optimize plasma generating conditions employed for a surface modifying method.
The present invention and its embodiments are described.
1. A method of surface treatment of a substrate having a void layer having void structure provided on a support comprising step of subjecting plasma treatment to the substrate.
2. The surface treatment method, wherein a functional group is provided with the substrate employing said plasma treatment.
3. The surface treatment method wherein void is roughened employing said plasma treatment.
4. The surface treatment method wherein the void layer contains particles, and the particles are roughened employing said plasma treatment.
5. The surface treatment method wherein said plasma treatment is carried out under an atmosphere comprised of an inert gas as the main component.
6. The surface treatment method wherein the void layer is provided at a portion furthest from the support.
7. The surface treatment method wherein the void layer is provided by coating.
8. The surface treatment method wherein at least one of the interior of the void layer and the surface layer of the void layer is subjected to a hydrophilic treatment employing said plasma treatment.
9. The surface treatment method wherein the surface layer of the void layer is subjected to a water repelling treatment employing said plasma treatment.
10. The surface treatment method wherein said plasma treatment is carried out employing corona discharge.
11. The surface treatment method wherein said plasma treatment is carried out under atmospheric pressure or similar pressure employing glow discharge.
12. The surface treatment method wherein a water repellent treatment is carried out after carrying out a hydrophilic treatment employing said plasma treatment.
13. The surface treatment method comprising a step of placing said substrate in a gas atmosphere and introducing said gas into said void structure, before said plasma treatment is carried out.
14. The surface treatment method wherein the substrate is ink-jet paper.
15. The surface treatment method wherein said plasma treatment is carried out by employing plasma generated in a pulse electric field.
16. The surface treatment method wherein step of subjecting plasma treatment to the substrate comprises steps of making gas plasma state, and introducing gas in the plasma state into said void structure.
17. The surface treatment method comprising steps of introducing gas in the plasma state into said void structure, before said plasma treatment is carried out wherein the plasma treatment is carried out by discharging on the substrate into whose void structure gas has been introduced.
18. A production method of an ink jet paper comprising a void layer having void structure provided on a support, wherein the method comprises a step of subjecting plasma treatment to the void layer.
19. The production method comprising step of forming a void layer on the support before said plasma treatment is carried out.
20. The production method of a base material, which comprises a void layer having a void structure, consists of the following steps: a step in which the void layer, having a void structure, is provided onto a support, and a step in which the void layer is subjected to plasma treatment.